Noise on my embedded asterisk pbx. Please help

Hi Folks,

i am a new member. i have been using asterisk for over a year now. first i used trixbox and now i have an embedded version, astlinux which uses asterisk 1.2

my hardware is as follows

200 mhz SIS cpu
128 mb onboard RAM

what is configured on my box

some SIP extensions
2 ITSP accounts

my problem

i use DISA by calling into my box to one voip trunk and then calling out with the other voip trunk. sometimes i get a constant noise starting with the astetrisk prompt for DISA pin all the way to the end of the call. there is no echo. it is more like a background stutter. i can still hear the voice and make out what someone is saying but it isnt good enough for me. this doesnt happen all the time. this happens like 1 out of 10 times maybe.

what’s happening and what can i do about it ?
i know my hardware is very modest. but then at any point of time there
is only one ITSP call being processed. my SIP calls always have pretty nice audio though even when there are 2 ongoing calls.

Thanks a lot.